The World Pride organisers have made mistakes and must share some of the blame for the current fiasco. However, they are not the sole villains. The Mayor of London, Boris Johnson, could have rescued Pride but has apparently chosen to not do so. The actions and inactions of the Greater London Authority (GLA) have compounded the problems that Pride now faces.

I speak with some authority; having helped organise Britain's first Gay Pride parade, held in London 40 years ago, in July 1972. I've attended every Pride since and I have been a Patron of Pride London for two decades.

This month is the 40th anniversary of the first ever Pride parade. Veterans from 1972 will lead Saturday's London march.

This major anniversary makes the shambles of Saturday's Pride parade, rally and parties all the more appalling.

A lack of official transparency and apparent economy with the truth at City Hall is part of the problem. Another issue is the Mayor's unwillingness to consult with the wider lesbian, gay bisexual and transgender (LGBT) community to find a solution.

City Hall has known about the problems for many weeks. Like Pride, the mayoral team failed to involve other LGBT stakeholders and financiers to raise extra cash and to draft a credible rescue plan. If the Mayor had acted weeks ago, we would not be in this mess.

I have received information from insiders at City Hall. There is concern about the behaviour of some officials connected to the Mayor and perhaps the Mayor himself.

Among other things, it is alleged as follows:

Corporate giants, Gaydar and Smirnoff, last week reportedly offered well in excess of £60,000 to cover Pride's funding shortfall but the Mayor's office spurned this offer claiming it was "too late". This "too late" claim is disputed, with some people suggesting that there was still sufficient time last week to produce a viable rescue package, if the Mayor's team had the will to do so.

Last year, the costs involved in the post-parade rally in Trafalgar Square were reportedly in the region of £50,000. This year they are allegedly £100,000. If true, it seems hard to justify a 100% increase which has, in part, created the funding shortfall.

It is claimed that the GLA is forcing Pride to use certain contractors, who are not necessarily the cheapest. This may be artificially exacerbating Pride's money problems.

The financial difficulties faced by Pride are mostly a cash-flow problem. The GLA has forced Pride to pay for everything upfront as a condition for the events to go head. Pride says the sponsorship money it expects to receive by the end of the festivities would have bridged most of the funding gap.

The GLA has reportedly not paid all the money it promised to Pride; thereby compounding the cash-flow difficulties.

The Mayor's office says there are "problems" and "safety issues" related to the Pride parade which require the start time to be bought forward to 11am and which require huge insurance premiums to be paid. However, they refuse to say what these problems and safety issues are. This is tantamount to demonising Pride as a troublesome event. In contrast, the police say it is one of the most trouble-free events held in London. Previously the police have adopted a very low presence, confident that Pride has no problem or safety issues.

Mayor Johnson's sudden change in the parade start-time from 1pm to 11am is very unfair to people who have pre-booked trains and coaches for a1pm start. The march will have left before many people have arrived. This is a recipe for chaos and disruption. Instead of an orderly march, tens of thousands of disorganised people will swarm through the streets towards Trafalgar Square and Soho, blocking traffic and causing grid-lock.

The 11am kick-off clashes with Jewish Sabbath services, which means that many Jewish people will be unable to attend. The lack of religious and cultural sensitivity by the mayoral team is surprising and shocking.

The Metropolitan Police are to be commended for their sympathetic, supportive relations with the Pride organisers. In contrast to City Hall and Westminster council, the police have gone out of their way to facilitate the Pride events, as much as possible given other official obstructions.

The Mayor's team has, in effect, gagged the Pride organisers by requiring them to submit all news releases to City Hall for approval. Changes in wording have been demanded by City Hall, which some say suit the spin the Mayor's office wants to put on the Pride fiasco. The Pride committee is not free to communicate with the LGBT community. It is alleged that Pride's contract with City Hall gives mayoral bosses a veto over what the Pride committee can and cannot say publicly.

Not only have the city authorities forced Pride to cancel all official street parties in Soho, they also want to stop any unofficial parties. Well over 100,000 people are expected to pour into Soho after the parade and rally. Westminster council has sent what reads like a threatening letter to gay venues warning them that their licences could be revoked if they play music that is "audible outside of your premises" and if they allow customers to drink in the street. Ignoring the exceptional circumstances on Saturday, venues are expected to operate on Saturday "as on any normal day." All celebrations must take place "within licensed premises," the letter says. Westminster council has not explained how up to 250,000 people are expected to cram into 20 Soho gay venues with a maximum capacity of 5,000 people.

No plans have been made by the Mayor or Westminster council to deal with the vast numbers of people expected on Saturday; apart from turning people away and dispersing them, which could lead to angry crowds and potential public order problems. This lack of contingency planning also risks creating traffic snarl-ups throughout central London, as crowds spill out into the streets with nowhere to go.

Cynics suggest that City Hall is not unhappy with all the bad publicity around Pride, in the hope that it will deter people from coming and keep the numbers low; making the festivities more manageable and easier to control.

Even though London is this year hosting World Pride, with LGBT delegations from around the world, the Mayor is not attending. Many LGBT people are interpreting his non-attendance as a snub. He did not attend last year either.

The Mayor's office demanded that Pride drop me as a keynote speaker at the post-parade rally in Trafalgar Square, giving the organisers the impression that if I spoke City Hall's authorisation for the entire rally could be withdrawn. Pride caved in to this pressure and informed me that I was being dropped from the speaker's list. When this was exposed at Mayor's Question Time on Wednesday, the Mayor agreed that I could speak, providing there were other political party speakers. He falsely claimed that I am a "Green politician". I am not a politician. I am not elected, or standing for election, to any public office. I'm a non-party-political human rights campaigner. I was planning to speak exclusively on LGBT issues, with no mention of the Green Party. The political affiliations of other rally speakers have not been questioned or used against them. I was singled out.

Watch Mayor's Question Time here.

Because of my exposure of this shambles, I expect the Mayor's office may find some new excuse to bar me from speaking on Saturday. City Hall has form. In previous years, I have been banned by Boris aides from attending mayoral LGBT events and receptions.

The decision to axe floats, buses and cars in the parade is disastrous for older and disabled LGBT people. Many will not now be able to participate. This is against the spirit of legislation intended to protect disabled and older people against exclusion and discrimination.

Banning floats in the parade is also a big blow to the many LGBT charities that have spent thousands of pounds on hiring and decorating them. They will lose a major opportunity to raise their profile, publicise their work and secure donation pledges.

Corporate bosses are already discussing a take-over of Pride. They are not displeased with the current failings. They see Pride as a commodity and a financial opportunity. They want to turn Pride into a largely depoliticised commercial event. The GLA is understood to be sympathetic to their interests. This would diminish the LGBT community links and betray the ideals and values of Pride.

It is difficult to say which of these problems have been compounded by the Mayor and which ones are the result of over-zealous officials.

Although I believe these allegations to be true, based on information I have received, they are, at this stage, allegations not proven facts. Nevertheless, they have more than a whiff of credibility and they demand open disclosure and honest answers from Mayor Johnson.

Regardless of the current shambles, the parade will go head. Without the floats and parties, it will revert to its roots - a protest march for LGBT human rights. The Pride slogan is: "Decriminalise homosexuality worldwide - Global equality for LGBT people." This is entirely appropriate, given that July is the 40th anniversary of the UK's first-ever Gay Pride parade.

The Mayor has a duty to help save Pride. If the event flops it will be a huge embarrassment to London, just three weeks before the Olympics.

I urge the mayor, police and Westminster council to re-open negotiations with the Pride organisers and other LGBT stakeholders to reinstate the start time of 1pm and to allow a small number of vehicles for older and disabled people.

For the sake of the many thousands of people expected to participate, and to avoid widespread disruption across central London, the city authorities have a public duty to make changes to ensure a happy, successful Pride.

For more info about Peter Tatchell's human rights campaigns: www.PeterTatchellFoundation.org